This invention relates to an erasable magneto-optical recording medium which is able to write, read and erase informations under the action of laser beam, and more particularly, it relates to a magneto-optical recording medium utilized for erasable magneto-optical recording.
Recently, attention has been increasingly paid to the magneto-optical recording in view of its high storage density, large storage capacity, arbitrary read-out, and reversible write/read. In magneto-optical recording, reversible magnetic domains are produced by irradiation of laser beam and bias external magnetic field on perpendicular magnetic thin films whose magnetization is perpendicular to the film surface. Corresponding to a direction of magnetization, two digital informations, such as "1" and "0", are recorded. Such recorded informations are read out by use of polar Kerr effect or Faraday effect.
Hitherto, perpendicular magnetic films such as rare-earth transition metal amorphous thin films have been proposed as a magneto-optical medium. The rare-earth-transition metal amorphous thin film (hereinafter referred to as "RE-TM amorphous film") has been considered to be suitable for a recording medium due to the following reasons: (1) it is a low noise medium because of no crystalline boundary in it, and (2) the ease of productivity of thin films in large area. The RE-TM amorphous films are disclosed, for example, in U.S. Pat. Nos. 4,126,494; 4,152,486; 4,569,881; 4,467,383; and 4,556,291; UK Patent Publication No. GB 2,071,696A; Japanese Kokai Patent Application Nos. 57-94948, 56-74843, and 58-73746; West German Offenlegungsschrift No. 3,317,101 Al; etc.
But, in the magneto-optical recording, since it is necessary to obtain sufficient read-out signals with a small recording domain in order to attain high speed and high density, the Kerr rotation angles in the magneto-optical recording films heretofore developed are still insufficient.
Among RE-TM amorphous films, relatively large Kerr rotation angles are obtained in amorphous films made of alloys using Tb element as a main rare-earth element such as Tb-Gd-Fe, Tb-Fe-Co, Tb-Gd-Fe-Co and the like alloys. But since the Tb element is expensive, there is a problem of making the cost of film per se higher.